During the past 40 years, the development of increasingly sophisticated computer hardware has led to a need for improved electronic cables capable of carrying more signals at high frequencies and at lower signal levels than ever before. In addition, increased sophistication of automated test equipment, aircraft, weapon systems, and telecommunications equipment such as satellites have increased the demand for high signal density multiconductor cable that is increasingly miniaturized and at the same time lighter in weight and capable of withstanding extreme temperature variations.
In these sophisticated systems, polytetrafluoroethylene (hereinafter PTFE) is preferred as an insulation because of its excellent dielectric properties, and thermal and chemical resistance. PTFE is also desirable as an insulation because of its ability to maintain mechanical integrity over a long period of time.
Typically the manufacture of flat multiconductor or ribbon cables require lamination with films, woven threads, or thermoplastic adhesives such as FEP (a copolymer of tetrafluoroethylene and hexafluoropropylene) to hold the multiconductors together and maintain their position in a flat plane.
Multiconductor flat or ribbon cable having at least one laminating film of PTFE insulation is known in the art. For example, U.S. Pat. No. 4,000,348 discloses a process to make flat multiconductor cable involving the lamination of fluorocarbon and similar high temperature resins. In addition, the patent describes a process for bonding and sintering unsintered extruded polytetrafluoroethylene (PTFE) containing a multiconductor cable with thermoplastic fluorocarbon resins and in turn to other materials including PTFE.
Alternatively, U.S. Pat. No. 4,443,657 discloses a cable construction having a plurality of conductors spaced apart in a planar relationship; a plurality of inner layers each surrounding one of the conductors, the inner layers formed of porous substantially unsintered polytetrafluoroethylene; a plurality of outer layers each substantially surrounding one of the inner layers, the outer layer being formed of impermeable sintered PTFE; and a plurality of webs, each connecting an outer layer to an adjacent outer layer, each of the webs being formed of impermeable sintered PTFE.
These products have limited functionality because of the limited ability to route individual conductors. The tapes, adhesives, and webs necessary to hold the multiconductor cable together also increase the weight of the cable as well as limit the functionality of the cable to certain temperature ranges where the bonding properties degrade.
There is a need for multiconductor cable that is capable of functioning over a wide temperature range and that is also lighter weight standard PTFE ribbon cable. There is also a need for a multiconductor cable construction where access to individual conductors is easily gained without disruption of the remaining conductors of the cable. Finally, it is also desired that previously achieved benefits from improvements in multiconductor cable construction such as flexibility and electrical performance are maintained.